This invention relates to a method for forming a titanate thin film on a silicon substrate. More particularly, this invention relates to a method that comprises depositing a metal film onto the silicon surface prior to deposition of the titanate film, which metal film is oxidized during annealing of the titanate film to inhibit formation of silicon dioxide and thereby increase the effective capacitance of the titanate film.
In the manufacture of microelectronic devices of the type that are based upon a silicon substrate, it is known to fabricate features that comprise a thin film of a dielectric material overlying the silicon surface. Such dielectric films are found, for example, in dynamic random access memory (DRAM), bypass capacitors and voltage variable capacitors. Silicon dioxide is commonly employed as a dielectric film for this purpose, but suffers from a low dielectric constant, K, that limits its usefulness, particularly in very thin films. It has been proposed to utilize a metal titanate film to take advantage of its relatively high dielectric constant. A preferred metal titanate film is composed of zirconium titanate, ZrTiO.sub.4. Zirconium titanate is suitably deposited by sputtering, but requires a high temperature anneal to develop the crystalline structure that displays the high dielectric constant and provides other desired electrical properties. This anneal is carried out in an oxidizing atmosphere to optimize the oxygen content and thereby improve the electrical leakage resistance of the film.
It is found that thin films of zirconium titanate formed immediately onto a silicon surface do not exhibit the high effective capacitance that is expected based upon the high dielectric constant of the bulk material. As used herein, effective capacitance refers to the capacitance per area measured between the substrate and an electrode affixed to the outer face of the dielectric film. The low effective capacitance is particularly observed for thin films having thickness less than about 500 A.degree.. It is now been found that this is due to the formation of silicon dioxide at the interface during oxygen annealing of the zirconium titanate.